Method and structure for large-footage excavation blasting of small-section tunnel by means of cental hole charging

Abstract

A method and structure for large-footage excavation blasting of a small-section tunnel by means of central hole charging. The structure comprises: a central hole (0) provided in the center of a tunnel section. Using the central hole (0) as the center, slot holes (1), auxiliary holes (2), and peripheral holes (3) are sequentially arranged from inside to outside on the tunnel section. The hole depth of the central hole (0) is greater than the hole depth of the slot holes (1), the hole depth of the slot holes (1) is greater than the hole depths of the auxiliary holes (2) and the peripheral holes (3), and the hole depths of the auxiliary holes (2) and the peripheral holes (3) are equal. In the central hole (0), a portion having a hole depth greater than the hole depth of the slot holes (1) forms a muck pushing blasting region. A muck pushing cartridge (4) that does not extend out of the muck pushing blasting region is mounted in the muck pushing blasting region, and a cartridge is mounted in each of the slot holes (1), the auxiliary holes (2), and the peripheral holes (3). The design of the structure layout is simple, the blast hole diameters are consistent, there is no need to replace a rock drilling device, the operability of on-site workers is high, and the utilization rate of the blast holes is high, so that tunnel excavation footage can be effectively increased, and tunnel excavation costs can be reduced.

Description

A method and structure for large-footprint tunneling blasting with empty hole charging in the center of a small-section tunnel Technical Field

[0001] The invention belongs to the technical field of underground tunnel excavation blasting, and in particular relates to a method and structure for large-footprint excavation blasting with empty charge in the center of a small-section tunnel. Background Art

[0002] Roadways are a crucial component of underground metal mining. After decades, or even centuries, of mining operations, some mines have seen their underground mineral resources gradually become deeper and more dispersed (previously, they mined rich ore and abandoned poor ore, now recovering low-grade ore). To fully recover these underground mineral resources and extend the mine's service life, a large number of roadways must be excavated to connect the entire mining system. Roadway excavation efficiency is a key factor influencing mine production efficiency and capacity. Efficient roadway excavation methods can shorten the construction time of mine development systems and the time to ore discovery, alleviate resource continuity and capacity decline issues faced by some established mining enterprises, and effectively reduce roadway excavation costs by increasing roadway excavation dimensions and reducing the number of excavation cycles (especially with digital electronic detonators). Due to factors such as underground tunneling equipment and processes, as well as tunneling costs, drill and blast remains the primary method currently used underground, especially for tunneling small-section roadways (less than 10m²). Because large tunneling equipment such as drilling rigs and charge trucks are not suitable, small shield tunneling equipment, such as the YT28 air-leg rock drill, is often used, with a 1.8-2.0m per shift. However, this method is rarely used in metal mine tunneling due to its low tunneling efficiency and high cost. Therefore, improving or optimizing tunneling processes is a key way to increase the efficiency of small-section roadways.

[0003] With the construction and development of underground mining in metal mines, people have adopted various methods to improve the utilization rate of blastholes and increase the advance of tunnels in one time in the drilling and blasting method for small-section tunnels.

[0004] Chinese patent application CN108060925A designs a hole arrangement method (wedge-shaped slotting) in which the slot holes are gradually concentrated from the hole mouth to the hole bottom toward the center hole, and implements a scheme of centralized charging and simultaneous detonation to improve the slotting blasting effect of small-section tunnels.

[0005] Chinese patent application CN110924957A designs a parallel slotting and hole arrangement structure with the tunnel centerline as the axis to improve the tunnel excavation progress and reduce material consumption costs.

[0006] Chinese patent application CN114909963A designs a spiral slot hole arrangement structure for blasting to provide more free space for the blasting slot, improve the utilization rate of the blasthole, optimize the blasting effect, and thus increase the excavation progress of small-section tunnels.

[0007] In all of the aforementioned patent applications, the optimal slot blasting effect is achieved by improving or optimizing the arrangement of the cut holes. This provides sufficient free (compensation) space for the subsequent blasting of auxiliary holes and peripheral holes, thereby increasing the advance of small-section roadways. However, the essence of improving the slot blasting effect is to form a sufficiently large cavity (free (compensation) space) after the cut holes are detonated. If the cavity volume is occupied by rock debris, the optimal slotting effect will still not be achieved, ultimately affecting the roadway excavation blasting effect and failing to achieve the maximum possible advance of the roadway. Summary of the Invention

[0008] The present invention solves the deficiencies of the prior art and provides a method and structure for large-footprint tunneling blasting with empty charge in the center of a small-section tunnel, which can increase the tunneling footage, reduce the number of cyclic tunneling times, increase the tunneling rate, and reduce the tunneling cost.

[0009] To achieve the above-mentioned purpose, the present invention first proposes a method and structure for large-footprint tunneling blasting with empty-hole charging in the center of a small-section tunnel, which specifically includes the following steps:

[0010] S1. Arrangement of blastholes for small tunnel section excavation:

[0011] A central hollow hole is arranged in the center of the tunnel section. On the tunnel section, groove holes, auxiliary holes and peripheral holes are arranged in sequence from the inside to the outside with the central hollow hole as the center. The depth of the central hollow hole is greater than that of the groove hole, and the depth of the groove hole is greater than that of the auxiliary hole and the peripheral hole. The depth of the auxiliary hole and the peripheral hole is the same.

[0012] S2. Design and charging of blasthole charge:

[0013] The charge amount of each hole is calculated based on the blasting volume. The top depth of the charge surface of the central empty hole is greater than the bottom depth of the charge surface of the slot hole. The slot hole, auxiliary hole and peripheral hole are filled with explosive bags.

[0014] S3. Design of the delayed explosion time of digital electronic detonators in each blast hole:

[0015] The order of controlling the detonation of the explosive charge is as follows: slot hole, central empty hole, auxiliary hole, and peripheral hole.

[0016] In this embodiment, four cutout holes are symmetrically arranged with the central hole as the center, and the multiple cutout holes form a prismatic cutout structure.

[0017] In this embodiment, adjacent auxiliary holes are arranged at equal intervals, and adjacent peripheral holes are arranged at equal intervals.

[0018] In this embodiment, in step S1, the apertures of the central hollow hole, the groove hole, the auxiliary hole and the peripheral hole are consistent, and the diameters are all d, unit: mm; the hole depth of the central hollow hole is h, unit: mm, the hole depth of the groove hole is h1, unit: mm, the hole depth of the auxiliary hole and the peripheral hole is h2, unit: mm, and h>h1, h1>h2.

[0019] In this embodiment, in step S2, the central empty hole does not need to be blocked, while the slot hole, auxiliary hole and peripheral hole blast hole blocking length is L1, L1 ≥ W d , where W d is the minimum resistance line length.

[0020] In this embodiment, in step S2, the charge amount of the central hole is , its charge The calculation process is as follows:

[0021] The explosion of the center hole explosive generates pressure: ;

[0022] Where, The pressure generated by the explosion of the central hole explosive, unit: Pa; For explosive power, ,in is the amount of gas detonation products, unit: mol, is the ideal gas constant, is the explosion temperature, unit: K; is the explosive packing density, ,in is the explosive charge mass, unit: kg, is the volume of the chamber, unit: L; is the van der Waals incompressible volume of the detonation products, unit: L;

[0023] The explosion of the central hole explosive generates pressure to push out the rock debris after the slot hole blasting.

[0024] Right now:

[0025] Where, is the cross-sectional area of ​​the hole, unit: m 2 ; is the mass of rock debris after slot blasting, unit: kg, ,in is the rock mass density, unit: kg / m 3 , is the spacing between the cutout holes, unit: cm; is the acceleration, unit: m / s 2 .

[0026] In summary, the charge amount of the central hole .

[0027] In this embodiment, in step S2, the charge amount of each hole of the slot hole and the auxiliary hole is and ,

[0028]

[0029] Where, The single hole charge of the slot hole, unit: kg; The single hole charge of the auxiliary hole, unit: kg; is the linear charge density per meter of blasthole, unit: kg / m, ,in is the charge diameter, unit: cm, is the density of explosives, unit: kg / m 3 ; is the blasthole depth, unit: m; is the charge coefficient;

[0030] The peripheral holes are blasted with smooth surface, and the charge per hole is :

[0031]

[0032] Where, The charge amount of a single hole in the peripheral holes, unit: kg; It is the charge density of smooth blasting hole line, unit: kg / m.

[0033] In this embodiment, in step S3,

[0034] The auxiliary holes are symmetrically divided into the first group of auxiliary holes and the second group of auxiliary holes with the central empty hole as the center, and the peripheral holes are symmetrically divided into the first group of peripheral holes and the second group of peripheral holes with the central empty hole as the center. The two diagonally arranged slot holes are set as a group with the central empty hole as the center. The detonation order of the central empty hole, the slot hole, the first group of auxiliary holes, the second group of auxiliary holes and the peripheral holes is as follows: the first group of slot holes is instantly detonated in the same section → delay t1 → the second group of slot holes is detonated in the same section → delay t0 → the central empty hole is detonated → delay t2 → the first group of auxiliary holes is detonated in the same section → delay t3 → the second group of auxiliary holes is detonated in the same section → delay t3 → the first group of peripheral holes is detonated in the same section → delay t3 → the second group of peripheral holes is detonated in the same section;

[0035] Detonation delay time of the first group of auxiliary holes , the calculation process is as follows:

[0036] ,

[0037]

[0038] Where, h1 is the depth of the cut hole, unit: mm; is the acceleration, unit: m / s 2 ;t 推 The slag pushing time after the center hole charge is detonated; are the initial velocities of rock debris after the slot hole blasting after the center hole blasting, t0, t1, t2, t3, unit: ms.

[0039] The present invention also includes a small-section tunnel blasthole layout structure, including a central empty hole arranged in the center of the tunnel section, and slot holes, auxiliary holes and peripheral holes arranged in sequence from the inside to the outside on the tunnel section with the central empty hole as the center. The depth of the central empty hole is greater than the depth of the slot hole, the depth of the slot hole is greater than the depth of the auxiliary hole and the peripheral hole, the depth of the auxiliary hole and the peripheral hole is the same, and the part in the central empty hole where the hole depth is greater than the depth of the slot hole forms a slag pushing blasting zone, and a slag pushing charge that does not extend out of the slag pushing blasting zone is installed in the slag pushing blasting zone, and the slot holes, auxiliary holes and peripheral holes are equipped with charge charges.

[0040] In this embodiment, a flexible metal mesh is fixedly hung 5 to 8 meters in front of the tunnel excavation working face and perpendicular to the tunnel direction to intercept the rock debris after the slot hole blasting, so that the blast pile is relatively concentrated and easy to remove.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) The present invention installs a slag pushing charge in the central hollow hole of the tunnel section, and the depth of the slag pushing charge makes the slag pushing charge farther away from the tunnel section relative to the bottom surface of the slot hole charge. This can, on the one hand, prevent the slag pushing charge from being affected by the slot hole blasting. On the other hand, during blasting, the slot hole is detonated first, and then the slag pushing charge is detonated, so that the rock debris after the slot hole blasting can be pushed out of the slot cavity by the blasting force of the slag pushing charge. In this way, sufficient free (compensation) space is provided for the subsequent auxiliary hole and peripheral hole blasting, thereby providing a guarantee for the successful implementation of large-footprint small-section tunnel excavation. The cross-section blasthole arrangement design of this method is simple, the blasthole diameter is consistent, and there is no need to replace the rock drilling equipment. The on-site workers have strong operability and high blasthole utilization rate, which can effectively increase the tunnel excavation footage and reduce the tunnel excavation cost.

[0043] (2) The depth of the slot hole is greater than that of the auxiliary hole and the peripheral hole. The depth of the auxiliary hole and the peripheral hole is the same. The extra-deep slot hole can relatively increase the depth of the slot cavity after blasting, increase the blasting free surface, and be beneficial to the blasting and rock breaking of the auxiliary hole and the peripheral hole, thereby improving the utilization rate of the blasthole and optimizing the blasting effect.

[0044] (3) The present invention increases the tunneling footage, reduces the number of cyclic tunneling times, improves the tunneling rate of small-section tunnels, and saves tunneling blasting costs (especially reducing the use of digital electronic detonators). At the same time, it is beneficial to shorten the construction time of the mine development system and the time to find the mine, and alleviate the problems of resource succession and production capacity decline of some old mining enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a schematic diagram of the arrangement structure of blastholes in a small-section tunnel according to the present invention;

[0046] FIG2 is a schematic diagram of the blasthole length in the present invention.

[0047] In the figure: 0, central empty hole; 1, slot hole; 2, auxiliary hole; 3, peripheral hole; 4, slag pushing package. Implementation Method

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0049] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0050] As shown in Figures 1 and 2, a method for high-speed tunneling blasting with empty charge in the center of a small-section tunnel is carried out in the following steps:

[0051] (1) Arrangement of blastholes for tunnel section excavation: Four slot holes are arranged in sequence around the central hole at the center of the tunnel section at equal distances from the central hole to form a prismatic slot structure; auxiliary holes and peripheral holes are arranged symmetrically on the tunnel section at equal intervals (see Figure 1); the diameters of the central hole, slot hole, auxiliary hole and peripheral hole are consistent, and the diameter is d (unit: mm); the depth of the central hole is greater than the depth of the slot hole, the depth of the slot hole is greater than the depth of the auxiliary hole and the peripheral hole, and the depth of the auxiliary hole and the peripheral hole is the same (see Figure 2); the depth of the central hole is h (unit: mm), the depth of the slot hole is h1 (unit: mm), the depth of the auxiliary hole and the peripheral hole is h2 (unit: mm), and h-h1 = (300~500) mm, h1-h2 = (200~300) mm;

[0052] (2) Design of blasthole charge and charge: Design the charge of the slag pack at the bottom of the central hole, as well as the charge in the slot hole, auxiliary hole and peripheral hole, and charge them separately; among them, the top depth of the charge surface of the central hole is greater than the bottom depth of the charge surface of the slot hole, and the central hole does not need to be blocked, while the slot hole, auxiliary hole and peripheral hole blasthole blocking length L1, L1 ≥ W d , where W d is the minimum resistance line length; when the diameter of the blasthole is 50mm, L1 is not less than 500mm;

[0053] Center hole charge The explosive blasting power must be greater than the weight of the rock debris after the slot hole blasting, and the rock debris after the slot hole blasting must be pushed out of the cycle excavation footage in an instant to provide enough free space for the auxiliary hole and surrounding hole blasting. The calculation process is as follows:

[0054] The explosion of the center hole explosive generates pressure:

[0055] Where, The pressure generated by the explosion of the central hole 0 explosive, Pa; For explosive power, ,in is the amount of gas detonation products (mol), is the ideal gas constant, is the explosion temperature (K); is the explosive packing density, ,in is the charge mass of explosive (kg), is the volume of the chamber (L); is the van der Waals incompressible volume of the detonation products, L;

[0056] The explosion of the central hole explosive generates pressure to push out the rock debris after the slot hole blasting, that is: Where, is the cross-sectional area of ​​the hole, m 2 ; is the mass of rock debris after slot blasting (kg), ,in is the rock mass density, is the spacing between the cut holes; is the acceleration, m / s 2 .

[0057] In summary, the charge of the central hole ;

[0058] Single hole charge of slot holes and auxiliary holes and It can be adjusted by the charge coefficient, which can be expressed as:

[0059] Where, is the charge amount of single hole of slot hole 1, kg; is the charge amount of auxiliary hole 2, kg; is the linear charge density per meter of blasthole (kg / m), ,in is the charge diameter (cm), is the density of explosive (kg / m 3 ); is the blasthole depth, m; is the charge coefficient;

[0060] The peripheral holes are blasted with smooth surface, and the charge per hole is It can be expressed as:

[0061] ;

[0062] Where, is the charge amount of the peripheral hole 3 per hole, kg; is the charge density of the smooth blasting hole line, kg / m;

[0063] (3) Design of the delayed detonation time of the digital electronic detonator for each blast hole: The digital electronic detonator is used to precisely control the detonation of the central empty hole charge, pushing out the rock debris after the slot hole blasting, forming sufficient supplementary space for the auxiliary hole and the peripheral hole blasting. Then, the digital electronic detonator is used to precisely control the symmetrical detonation of the auxiliary hole and the peripheral hole one by one.

[0064] The auxiliary holes are symmetrically divided into a first group of auxiliary holes and a second group of auxiliary holes with the central empty hole as the center, and the peripheral holes are symmetrically divided into a first group of peripheral holes and a second group of peripheral holes with the central empty hole as the center. The two diagonally arranged slotted holes are set as a group with the central empty hole as the center. The order of detonating the digital electronic detonators in the central empty hole, the slotted hole, the first group of auxiliary holes, the second group of auxiliary holes and the peripheral holes is as follows: the first group of slotted holes is instantly detonated in the same section → delay t1 → the second group of slotted holes is detonated in the same section → delay t0 → the central empty hole is detonated → delay t2 → the first group of auxiliary holes is detonated in the same section → delay t3 → the second group of auxiliary holes is detonated in the same section → delay t3 → the first group of peripheral holes is detonated in the same section → delay t3 → the second group of peripheral holes is detonated in the same section;

[0065] After the slot holes are detonated, the central empty hole is detonated again to push the rock debris after the slot hole blasting out of the cycle excavation footage. Then, the first group of auxiliary holes are detonated again. At this time, the delay time of the digital electronic detonator of the first group of auxiliary holes is , the calculation process is as follows:

[0066] ,

[0067] Where, h1 is the depth of the cut hole, unit: mm; is the acceleration, unit: m / s 2 , It is the slag pushing time after the empty-hole charge is detonated; The initial velocity of the rock debris after the slot hole blasting after the center hole blasting, t0, t1, t2, t3, unit: ms, t1, t3 are empirical values, generally 25ms.

[0068] (4) A flexible metal net is pre-fixed and hung perpendicular to the direction of the tunnel at a position of 5 to 8 m in front of the tunnel excavation working face (before blasting) to intercept the rock debris pushed out after the slot hole blasting, so that the blast pile is relatively concentrated and the slag is easy to remove. Example

[0069] Taking a tungsten mine tunnel excavation blasting project as an example, the tunnel cross-section size is 2.5×2.5m 2 ;

[0070] The specific blasting steps are as follows:

[0071] (1) Arrangement of blastholes for tunnel section excavation: Four slot holes are arranged in sequence around the central hole at the center of the tunnel section at equal distances from the central hole to form a prismatic slot structure; auxiliary holes and peripheral holes are arranged symmetrically on the tunnel section at equal intervals (see Figure 1); the diameters of the central hole, slot hole, auxiliary hole and peripheral hole are consistent, all with a diameter of 40 mm; the depth of the central hole is greater than that of the slot hole, the depth of the slot hole is greater than that of the auxiliary hole and the peripheral hole, and the depths of the auxiliary hole and the peripheral hole are the same; the depth of the central hole is 3200 mm, the depth of the slot hole is 2700 mm, and the depth of the auxiliary hole and the peripheral hole is 2500 mm;

[0072] (2) Design and charging of blasthole charges: Design the charge of the slag pack at the bottom of the central hole, as well as the charge in the slot holes, auxiliary holes and peripheral holes, and charge them separately; the charge of the central hole is 0.45 kg, the charge of the slot holes and auxiliary holes is 3.15 kg, and the charge of the peripheral holes is 0.375 kg; the central hole does not need to be blocked, while the slot holes, auxiliary holes and peripheral holes are blocked with a length of 500 mm;

[0073] (3) Design of the delayed detonation time of the digital electronic detonator for each blast hole: The digital electronic detonator is used to precisely control the detonation of the central empty hole charge, pushing out the rock debris after the slot hole blasting, forming sufficient supplementary space for the auxiliary hole and the peripheral hole blasting. Then, the digital electronic detonator is used to precisely control the symmetrical detonation of the auxiliary hole and the peripheral hole one by one.

[0074] Specifically, the auxiliary holes are divided into the first group of auxiliary holes and the second group of auxiliary holes with the vertical line passing through the central hole and extending along the tunnel section as the center. The order of detonating the digital electronic detonators in the central hole, the slot hole, the auxiliary hole and the peripheral holes is as follows:

[0075] The first group of slot holes are detonated instantly at the same stage → delay → The second set of slot holes was detonated at the same stage → Delay →Center hole detonation →Delay → Detonate the first group of auxiliary holes in the same section → Delay 100ms → Detonate the second group of auxiliary holes in the same section → Delay 125ms → Detonate the first group of peripheral holes in the same section → Delay 150ms → Detonate the second group of peripheral holes in the same section; Tunnel excavation blasting is divided into 7 sections with delayed detonation;

[0076] (4) A flexible metal net is pre-fixed and hung perpendicular to the direction of the tunnel at a position of 5 to 8 m in front of the tunnel excavation working face (before blasting) to intercept the rock debris pushed out after the slot hole blasting, so that the blast pile is relatively concentrated and the slag is easy to remove.

[0077] The traditional small-section excavation method has an excavation footage of 1.8~2.0m. In Example 2, the excavation footage reaches 2.5m, and the blasting utilization rate is as high as 95%. In long-distance tunnel excavation, it can effectively shorten the number of tunnel excavation blasting cycles, increase the speed of tunnel excavation, reduce the cost of tunnel excavation, and bring better economic benefits to the mine.

[0078] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. All equivalent structural transformations made based on the contents of the present invention's description and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for large-scale excavation blasting with empty charge in the center of a small-section tunnel, characterized in that: The following steps are involved: S1. Arrangement of blastholes for small tunnel section excavation: A central hollow hole is arranged in the center of the tunnel section. On the tunnel section, groove holes, auxiliary holes and peripheral holes are arranged in sequence from the inside to the outside with the central hollow hole as the center. The depth of the central hollow hole is greater than that of the groove hole, the depth of the groove hole is greater than that of the auxiliary hole and the peripheral hole, and the depths of the auxiliary hole and the peripheral hole are the same; S2. Design and charging of blasthole charge: The charge amount of each hole is calculated according to the blasting amount. The top depth of the charge surface of the central empty hole is greater than the bottom depth of the charge surface of the slot hole. The slot hole, auxiliary hole and peripheral hole are filled with explosive bags. S3. Design of the delayed explosion time of digital electronic detonators in each blast hole: The order of controlling the detonation of the explosive charge is as follows: slot hole, central empty hole, auxiliary hole, and peripheral hole.

2. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: Four slot holes are symmetrically arranged with the central hole as the center, and the multiple slot holes form a angular columnar slot structure.

3. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: Adjacent auxiliary holes are arranged at equal intervals, and adjacent peripheral holes are arranged at equal intervals.

4. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: In step S1, the hole diameters of the central hollow hole, the groove hole, the auxiliary hole and the peripheral holes are consistent, and the diameters are all d, unit: mm; the hole depth of the central hollow hole is h, unit: mm, the hole depth of the groove hole is h1, unit: mm, the hole depth of the auxiliary hole and the peripheral hole is h2, unit: mm, and h>h1, h1>h2.

5. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: In step S2, the central empty hole does not need to be blocked, while the slot hole, auxiliary hole and peripheral hole blast hole blocking length is L1, L1 ≥ W d , where W d is the minimum resistance line length.

6. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: In step S2, the charge amount of the central hole is , its charge The calculation process is as follows: The explosion of the hollow center explosive generates pressure: ； In the formula, The pressure generated by the explosion of the central hollow explosive, unit: Pa; For explosive power, ,in is the amount of gas detonation products, unit: mol, is the ideal gas constant, is the explosion temperature, unit: K; is the explosive packing density, ,in is the explosive charge mass, unit: kg, is the volume of the chamber, unit: L; is the van der Waals incompressible volume of the detonation products, unit: L; The explosion of the central hole explosive generates pressure to push out the rock debris after the slot hole is blasted. Right now: ； In the formula, is the cross-sectional area of ​​the hole, unit: m 2 ; is the mass of rock debris after slot hole blasting, unit: kg, ,in is the rock mass density, unit: kg / m 3 , is the spacing between the slot holes, unit: cm; is the acceleration, unit: m / s 2 , In summary, the amount of charge in the central hole ： 。 7. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 1 is characterized in that: In step S2, the charge amount of each hole of the slot hole and the auxiliary hole is and , ； In the formula, The charge amount of a single hole of the slot hole, unit: kg; The single hole charge of the auxiliary hole, unit: kg; is the linear charge density per meter of blasthole, unit: kg / m, ,in is the charge diameter, unit: cm, is the density of explosives, unit: kg / m 3 ; is the blasthole depth, unit: m; is the charge coefficient; The peripheral holes are blasted with smooth surface, and the charge per hole is ： ； In the formula, The charge amount of the peripheral holes per hole, unit: kg; It is the charge density of smooth blasting hole line, unit: kg / m.

8. The method for large-scale excavation blasting with empty charge in the center of a small-section tunnel according to claim 2 is characterized in that: In step S3, The auxiliary holes are symmetrically divided into the first group of auxiliary holes and the second group of auxiliary holes with the central empty hole as the center, the peripheral holes are symmetrically divided into the first group of peripheral holes and the second group of peripheral holes with the central empty hole as the center, and the two diagonally arranged slotted holes are set as a group with the central empty hole as the center, and the detonation sequence of the central empty hole, the slotted hole, the first group of auxiliary holes, the second group of auxiliary holes and the peripheral holes is: the first group of slotted holes is instantly detonated in the same section → delay t1 → the second group of slotted holes is detonated in the same section → delay t0 → the central empty hole is detonated → delay t2 → the first group of auxiliary holes is detonated in the same section → delay t3 → the second group of auxiliary holes is detonated in the same section → delay t3 → the first group of peripheral holes is detonated in the same section → delay t3 → the second group of peripheral holes is detonated in the same section; Detonation delay time of the first group of auxiliary holes , the calculation process is as follows: ， ； ； Where, h1 is the depth of the slot hole, unit: mm; is the acceleration, unit: m / s 2 , t 推 The slag pushing time after the center hole charge is detonated, unit: ms; are the initial velocities of rock debris after the central hole blasting and the slot hole blasting, t0, t1, t2, t3, unit: ms.

9. A small-section tunnel blasthole layout structure, characterized in that: It includes a central empty hole arranged in the center of the tunnel section, and slot holes, auxiliary holes and peripheral holes are arranged in sequence from the inside to the outside on the tunnel section with the central empty hole as the center. The depth of the central empty hole is greater than the depth of the slot hole, the depth of the slot hole is greater than the depth of the auxiliary holes and the peripheral holes, the depths of the auxiliary holes and the peripheral holes are the same, and a slag pushing blasting zone is formed in the part of the central empty hole where the hole depth is greater than the hole depth of the slot hole, and a slag pushing explosive bag which does not extend out of the slag pushing blasting zone is installed in the slag pushing blasting zone, and explosive bags are installed in the slot holes, auxiliary holes and peripheral holes.

10. The small-section tunnel blasthole arrangement structure according to claim 9, characterized in that: A flexible metal mesh is fixedly hung 5 to 8 meters in front of the tunnel excavation working face and perpendicular to the direction of the tunnel.

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